Isopropyl benzene, also known as cumene, is a bulky chemical intermediate for manufacturing phenol, acetone, and α-methyl styrene. In the industry, isopropyl benzene is produced by the alkylation of benzene with propylene. The main byproduct of the alkylation is poly-isopropyl benzene. Early in 1945, the UOP Company has published a method (SPA method) for producing isopropyl benzene from propylene and benzene under the presence of acid catalyst (U.S. Pat. No. 2,382,318). SPA process uses solid phosphoric acid as the alkylation catalyst. Because solid phosphoric acid cannot catalyze transalkylation, the SPA process does not comprise transalkylation unit. Therefore, the SPA process can only run under relative high molar ratio of benzene to propylene (in a range of 5˜7), also the yield of isopropyl benzene is less than 95%. In the 1980s, the Monsanto Company developed the technique for manufacturing isopropyl benzene under the presence of the alkylation catalyst AlCl3 and realized the industrial application thereof. Because AlCl3 cannot catalyze transalkylation either, the yield of isopropyl benzene from AlCl3 method is still low. Moreover, AlCl3 itself can cause severe pollution and corrosion.
In the 1990s, companies including Dow, CD Tech, Mobil-Badger, Enichem and UOP successively disclosed the fixed bed process using microporous zeolite as catalysts, which is capable of transalkylation. In the prior art, benzene and propylene first react in an alkylation reactor, producing isopropyl benzene and poly-isopropyl benzene; and after being separated in a rectification system, the poly-isopropyl benzene mixes with benzene and the mixture is fed into a transalkylation reactor with a single catalyst bed for transalkylation.
In the existing technology for producing isopropyl benzene, the alkylation of benzene with propylene usually occurs in a single fixed bed reactor comprising a plurality of stages, applying technologies including staged feeding of propylene and external circulation of reaction liquid. The benzene to propylene ratio is usually larger than 2.0. In fact, the benzene to propylene ratio in most cumene factory is larger than 3.0. When benzene to propylene ratio is to be further reduced to 2.0 or lower, it encounters rapid deactivation of the catalyst (caused by high concentration of propylene), or insufficient propylene conversion (caused by excessive external circulation), or much impurity n-propyl benzene in the product (caused by over high reaction temperature). The above technical obstacles restrict the further reduction of benzene to propylene ratio. U.S. Pat. No. 6,835,862B1 discloses an optimization process using relatively high external circulation volume of reaction liquid to reduce the deactivation rate of the catalyst. However, with the process of a single reactor, high external recycle ratio cannot solve the above three contradictory problems simultaneously.